A glass chopped strand mat is generally obtained by the method described below.
(1) Several ten to several hundred glass single fibers (with a fiber diameter of around 10 μm) are bundled with a sizing agent to form a glass strand.
(2) The glass strand is chopped into a predetermined length, so that bundled glass chopped strands are obtained.
(3) The glass chopped strands are scattered in random directions on a transport net to form a laminate.
(4) A binder powder is scattered on the laminate and heated in an oven chamber, so that the glass chopped strands are bonded together with the binder to form a glass chopped strand mat.
In conventional techniques, an unsaturated polyester resin is often powdered by mechanical pulverization and used for the binder (see for example Patent Document 1).
Patent Document 1: Japanese Patent Application Laid-Open (JP-A) No. 2003-48255
However, conventional binders have a wide particle diameter distribution, and therefore, not all of the particles are suitable for the adhesion to a laminate of glass chopped strands. Specifically, particles with a significantly small diameter scattered on the laminate adhere only to the surface layer of the laminate and can hardly reach the inside and the back side layer of the laminate. As a result, the entire binding between glass fibers may be insufficient, so that a hard mat of low quality can be obtained. On the other hand, particles with a significantly large diameter may often fall through the interstices between the laminated strands without adhering to the laminated strands. As a result, a problem may occur in which the binder must be supplied in an amount larger than the amount originally required for the performance of the mat, such as strength.